Pressure sensitive tapes having a fabric layer between two or more polymeric layers (such as films, adhesives, etc.) are well known. Previous efforts to create these types of pressure sensitive tapes have, in large part, included a woven substrate as the textile component. Such substrates are susceptible to raveling along the cut edges of the finished tape. For this reason, woven substrates used in tapes are generally treated at the edges, for example, by tucking the edges or otherwise sealing them, to minimize this problem.
More recently, it was discovered that an acceptable tape substrate could be manufactured using a weft-inserted warp knit fabric as the textile reinforcing component. Generally, the existing weft-inserted warp knit fabric performs well for its intended purposes. It is easily torn in both horizontal and vertical directions, and it adheres well to a wide variety of surfaces. Such a tape is described in U.S. Pat. No. 5,017,425, which is incorporated herein by reference.
Despite its acceptable performance, the previous weft-inserted warp knit fabric exhibits several problems that are the result of the fabric's relative lack of dimensional stability. Because the chain stitches in the weft-inserted warp knit fabric run vertically through the fabric without any interlocking between chains, there is a tendency for the yarns to shift horizontally during manufacture of either the fabric or the tape. As a result, two situations are observed. First, it is difficult to handle the fabric substrate after it is wound onto a take-up roll without shifting the stitch yarns. Second, because of the fabric's shifted yarns, the finished tape often lacks uniform internal geometry, a visually apparent flaw that, if severe, can result in the finished tape being rejected as “off-quality.”
Another problem results from the fabric's relative lack of dimensional stability. This issue is known as “stringing,” a condition that occurs during processing if the film that provides the outer surface of the tape is not properly aligned with the fabric. In this situation, the raw edges of the fabric are left exposed, and the loose yarns (that is, those not secured to the film) slide off the fabric as it passes over the calendar roll. As the master roll is wound, these loose ends on the edges of the fabric can become tangled with one another or, even worse, can become adhered to the adhesive side of the roll. In many instances, especially when the strings on the edge of the fabric become adhered to the underside of the tape, the stringing is so significant that the smaller rolls made from the outermost edges of the master roll must be discarded. This waste is a significant problem for tape manufacturers.
One contemplated approach for solving the stringing problem is to include a plurality of tricot stitches in the weft-inserted warp knit fabric substrate. This has the effect of locking adjacent wales together, so that shifting and stringing are substantially reduced. However, replacing all of the chain stitches with tricot stitches results in a condition commonly known as “neck-down”, in which the fabric telescopes or collapses inward on itself to create a narrower than desired width. Clearly, this tendency would not be acceptable in production of a flat tape that must be rolled up on itself for packaging. As a further complication, a tricot knit fabric is more likely to be difficult to tear uniformly.
The present disclosure addresses and overcomes these problems.